Hentai is animated or drawn pornography originating from Japan, many people hate hentai and they think that its sick,there is nothing wrong with hentai, its not like your watching nasty stuff, its still girls (Well some of it is with the exception of Yaoi Futanari
which I personally don't care for, but aren't judging people who are in to that thing even though it is kind of weird.
These are the most common examples for people thinking hentai is gross:
"There not real"
Thats about the same as saying all documentaries are superior to fictional movies because they aren't real. In porn they are also very photoshopped and make up-ed
"Some old sweaty guy probably drew it"
Your not masturbating to an old sweaty guy, porn is also directed by 50 year old men most of the time.